Microscopic changes governing melting anisotropy: Real-time nanosecond x-ray diffraction

To understand the microscopic origins governing melting anisotropy, in situ x-ray diffraction (XRD) measurements were obtained in aluminum single crystals shocked along $\ensuremath{\langle}100\ensuremath{\rangle}$ and $\ensuremath{\langle}110\ensuremath{\rangle}$ to stresses below and above the melting threshold for each orientation. XRD results and analysis for the two orientations showed significant differences in the microstructure prior to the melting threshold stresses, demonstrating the key role of deformation induced microstructure---in addition to temperature and pressure---on the melting transition. Our findings make a strong case for reconsidering theoretical approaches to melting, specifically for dislocation mediated melting, in shock compressed solids.